We propose to conduct a prospective investigation of dietary, physical activity, female hormones and other etiologies of hip and forearm fractures among men and women. The study will take advantage of ongoing prospective cohorts of 121,700 women aged 40-65 years and 52,000 men aged 40-75 years in 1986. Both groups are followed every two years; extensively validated dietary questionnaires were completed in 1980, 1984, and 1986 by approximately 85,000 women and by all men in 1986. Physical activity was assessed in 1980, 1986 and every two years. Hormone replacement therapy has been assessed throughout the Nurses' Health Study. Fractures of the hip or forearm are ascertained on the biennial followup questionnaires; for women we have used supplementary questionnaires to further characterize the fractures occurring in 1980-1990 according to circumstance level of trauma. In the proposed study we will mail similar supplementary questionnaires to men and women reporting fractures on the 1992 and 1994 questionnaires. Based on data collected so far, we expect a total of 1,851 and 358 hip fractures in women and 526 forearm and 328 hip fractures in men. Hypotheses to be addressed using information already collected prospectively include that dietary calcium and vitamin D (including supplements) during adulthood and consumption of milk and other dietary products before age 20 are associated with reduced risk of fractures, and that higher phosphate, protein, caffeine, alcohol, and carbonated beverage intakes are associated with increased risk. We will also examine and quantify the relation of several well established determinants of fractures such as estrogen replacement therapy (including duration of use), and relative weight at different ages, waist and hip circumferences, and address hypotheses related to physical activity, thiazide use, and (among women) parity. In addition, we will conduct nested case-control analyses using toenail specimens collected in 1982 from 68,000 women and in 1987 from 33,400 men to evaluate the hypothesis that increased fluoride intake reduces the risk of fractures. Stratified and multivariate techniques will be used to quantify the risk of hip and forearm according to the level of dietary factors and other variables after controlling for potentially important confounding variables. In the analyses we will specifically examine associations by gender and by fractures type (forearm fractures, being most closely related to Type I osteoporosis, and hip fractures, representing Type II osteoporosis).